The present invention relates to a throwaway tip or insert adapted to be used for cutting tools, such as face cutters, and more particularly to a throwaway insert adapted to be suitably mounted on a tool body of a vertical cutting edge type face cutter so that either one of a first (or upper) and a second (or lower) major faces of the insert, disposed in parallel and opposite to each other, is located so as to constitute a flank which faces toward the external circumference of the tool body.
Recently, in the art of conventional cutting tools such as face cutters, especially for cutting high hardness material and hard-to-machine material such as stainless steel, a so-called vertical cutting edge type cutting tool is widely used, because of high tool rigidity being secured thereby, in that throwaway inserts of a flat shape type are mounted on the tool body so that either one of an upper and a lower major faces of the insert, disposed in parallel and opposite to each other, is located so as to constitute a flank which faces toward the external circumference of the tool body.
Shown in FIGS. 11 to 15 is an insert 10 adapted for such a vertical cutting edge type face cutter is, which has a rectangular flat plate configuration, and comprises a first (or upper) and a second (or lower) major faces 12 and 14 disposed parallel and opposite to each other in the direction of the thickness of the flat plate; a first pair of oppositely facing side faces 21 and 22 extending between the two opposite side margins of the first major face 12 and two opposite side margins of the second major face 14; and a remaining second pair of oppositely facing side faces 23 and 24 extending between remaining two side margins of the first major face 12 and remaining two side margins of the second major face 14. A first pair of major cutting edges 25, 25 and a second pair of major cutting edges 25, 25 are respectively constituted along each of the intersections of the first major face 12 with each of the first pair of side faces 21 and 22, and the intersections of the second major face 14 with the first pair of side faces 21 and 22. Minor flanks 26, 26, 26, 26 are respectively formed along each of the intersections of the second pair of side faces 23, 24 with the first and second major faces 12, 14, extending between the opposite intersections of the major faces and the side faces where the intersection constitutes a major cutting edge. Also, minor cutting edges 30, 30, 30, 30 are respectively constituted along the intersections of one end of the minor flanks 26, 26, 26, 26 with the side faces 21 and 22.
The minor flanks 26, 26, 26, 26 are respectively formed by beveling the intersections of the major faces 12, 14 and second side faces 23, 24 at a predetermined angle, to constitute a slant face which recesses inwardly as the minor flank proceeds from the one end thereof, where the minor cutting edges 30 is formed, toward the other end thereof, whereby each of the minor cutting edges 30 is provided with a predetermined insert relief angle .phi..sub.c. Hereby, an insert relief angle .phi..sub.c means a slant angle between the minor flank and an imaginary intersection 32 which would be formed between the major face 14 and the side face 23 if the slant minor flank 26 were not formed. The insert 10 is provided with a bolt hole 11 through which a bolt B shown in FIG. 17 is inserted to secure the insert 10 to a tool body 35 shown in FIG. 17.
As shown in FIGS. 16 and 17, the insert 10 formed as above is mounted, and secured with the bolt B, on a mounting seat 40 disposed on an external circumference at the front end of the tool body 35 having a substantially circular configuration, so that a predetermined corner angle .theta. is provided to the insert 10 so mounted, to be used for cutting a workpiece (not shown). When mounted, the insert 10 is selectively located on the mounting seat 40 so that either of the first or second major faces 12, 14 is positioned to constitute an external circumference flank which faces toward the external circumference of the tool body 35. In FIGS. 16, 17 the first major face 12 is selected to be the flank. One of the second pair of the side faces 23, 24 facing toward the rear of the tool body 35 in the axial direction of the tool body 35 (23 in the case of FIGS. 16, 17) and one of the first side faces 21, 22 facing opposite the direction of rotation of the tool body 35 (21 in the case of FIGS. 16, 17) are respectively faced and in contact to insert positioning reference faces 43, 41 of the mounting seat 40, to serve as the positioning reference face on the insert side, and also the supporting surface during the cutting operation.
The conventional insert 10 described above has a disadvantage. With respect to the conventional insert, it is known that the length L of the major cutting edges 25, 25, 25, 25 shown in FIG. 11 is made shorter since the other (or rear) end of the minor flank 26 reaches the intersection of the major face, 12 or 14, and the side face, 21 or 22, on which the major cutting edge is formed, whereby a maximum cutting depth .delta. of the insert 10, shown in FIG. 16, reduces. The conventional insert 10 described above also has another disadvantage. With respect to the conventional insert, it is known that the surface area of the second pair of the side faces 23, 24 is greatly decreased since the formation of the minor flank 26 removes substantial portions of the side faces 23, 24, whereby the stability of the insert 10 on the tool body 35 is adversely decreased.